The invention relates to an apparatus and a method for producing a nonwoven fabric from fibers.
Such nonwoven fabrics are used in particular for producing compression-molded parts, insulating mats, and upholstery material.
Essentially two methods and corresponding apparatuses are known for producing such nonwoven fabrics: forming a nonwoven fabric by means of carding/combing machines, and aerodynamic nonwoven fabric forming systems.
The disadvantages of both systems are low or even very low throughputs and thus high costs, as well as the necessity of using at least extensively cleaned fibers that are free of foreign bodies and have been opened and that are therefore expensive.
Although carding/combing machines are capable of producing especially fine, uniform nonwoven fabrics, nevertheless they make the most stringent demands in terms of freedom from shives and the degree of opening of the fibers. Their production output, at a maximum of 500 kg/h, is very low, and the costs are correspondingly high.
If bast fibers that still contain shives are processed, for instance, they catch on the card clothings of carding/combing machines or become deposited in the bores of holes of the screen drums or screen belts of aerodynamic nonwoven fabric forming systems and hinder the nonwoven fabric formation considerably, even to the extent of complete inoperability.
In the ensuing needling, hemp shives in particular deflect the needles from the bores in the perforated plates onto the steel plates. As a consequence, the needles break.
Aerodynamic nonwoven fabric forming systems make less stringent demands in terms of freedom from shives and the degree of opening of fibers. The output reaches about 1000 kg/h. This is still inadequate, however, to attain favorable costs from mass-produced products.
Cleaning the fibers of shives and opening the fibers are associated with high costs. Furthermore, cleaning the fibers, and especially opening them, always leads to more or less severe mechanical damage to the fibers. This entails material losses of up to 40%. In the final analysis, well-cleaned and opened fibers that thus meet these demands made of the known systems can be created only from retted hemp or flax straw. Retting, however, is a biodegrading process and thus inevitably weakens the fibers as well. For industrial purposes, fibers with maximum strength and a maximum modulus of elasticity are required.
Other systems for forming bulk goods are used for manufacturing boards of wood material; the final products are in particular particle boards that have gained extensive use in furniture making. Scattering methods are used to produce such plates, and in these methods the chips are delivered from a bunker to a feed roller head and from there are scattered onto a substrate by way of various intermediate processing stages. One such scattering method is described in German Patent Disclosure DE-A 4 128 592, which shows the closest prior art. However, this technique can be used only with chips that flow easily. The flowability of the chips has the major disadvantage, however, that hardening and compacting must be done immediately after the scattering; that is, once again, additional processing stations are required to achieve an easily handled product. The aforementioned wide range of end products (insulating materials, molded upholstery parts, compression-molded parts) cannot be made with the chip cakes produced by this method.
The object of the present invention is thus to produce nonwoven fabrics for insulating purposes, upholstery materials, and the like which are distinguished by minimal costs. In particular, the object is also to produce nonwoven fabrics from which molded parts with a high modulus of elasticity and high strength are created.
In a similar way, via the second nozzles 60, it is possible to apply a sealing agent to the nonwoven fabric 70 as it forms, or to apply an adhesive for the sake of better adhesion of the nonwoven fabric 70 to the first coating belt. A previously foamed material or an unfoamed material with an incorporated propellant may be used as the sealing agent and binds to the surface of the nonwoven fabric 70 that is to be coated.
The fundamental concept of the invention is based on the fact that minimal costs are attainable only if the number of production stages is reduced to a minimum and the throughput is maximized. Furthermore, the currently usual material losses should at least be decisively lowered.
As already mentioned above, the production stages of xe2x80x9cseparating shivesxe2x80x9d or similar substances in granulate or nodelike form that accompany fibers, and xe2x80x9copeningxe2x80x9d (refinement) are extraordinarily cost-intensive. Aside from the incident operating costs, the material losses that they cause have a major effect on cost.
According to the invention, nonwoven fabrics can now be produced in which the two aforementioned production stages, namely xe2x80x9cshive separationxe2x80x9d and xe2x80x9cfiber openingxe2x80x9d are no longer needed, since with this method and the corresponding apparatus according to the invention, in an extreme case even uncleaned and unopened fibers can be processed. The attendant production costs are thus dispensed with.
High fiber strength and a high modulus of elasticity are furthermore obtainable only if retting is dispensed with. Dispensing with retting, however, means that the fibers have a much high shive content and are much coarser and rougher than is required for processing as in the prior art. Once again, the invention is still usable, unlike nonwoven fabric forming systems of the prior art, which cannot function at all with unretted, uncleaned and unopened fibers.
It is especially advantageous, however, that the attendant material losses are also avoided, which in terms of cost makes even more of a difference.
The apparatus according to the invention is furthermore capable of providing a yield that is multiple times greater than in prior art systems. Costs are thus reduced to a fraction.
According to the invention, unretted, uncleaned, unopened fibers with lengths between 20 and 150 mm, preferably 30 to 70 mm, with or without shives and/or nonfibrous components that still stick to them and/or are located or scattered freely between them, with or without recycled polymer and other fibers, can thus be formed into a single- or multi-layer nonwoven fabric, and a throughput that is far above the prior art is attained, namely from 2000 to 9000 kg/h, preferably 2000 to 4000 kg/h, for a working width of 3000 mm.
However, the method according to the invention is usable when any fibers are used, even synthetic, mineral or natural fibers, including and cleaned and opened fibers, and so forth.